Effect of maternally-derived immunity in the development of humoral immune responses to vaccination and subsequent challenge with BVDV
Type of DegreeDissertation
Veterinary Clinical Sciences
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Bovine viral diarrhea virus (BVDV) is a viral pathogen of cattle that can present with different clinical syndromes including reproductive failure, immunosuppression, respiratory disease, and gastrointestinal disease. Significant economic losses have been associated with the clinical presentation of BVDV in cattle operations worldwide. BVDV has been identified as an important contributor in the bovine respiratory disease complex (BRDC) in calves due to its ability to cause immunosuppression and act in synergism with other viruses and bacteria. Vaccination of young calves against BVDV is considered an important management practice to prevent losses associated with acute BVDV infection and BRDC. Previous research has demonstrated that maternally-derived antibodies to BVDV can protect against acute BVDV infection. When maternal antibodies start to decay and disappear, calves become susceptible to infection and disease; however, the duration of maternally-derived immunity is variable among young calves and some calves become susceptible to BVDV infection earlier in life than others. Additionally, the presence of maternally-derived antibodies in calves at vaccination interferes with the induction of adequate antibody responses and can affect the prevention of viremia and BVDV shedding. This research is concentrated on the evaluation of duration of maternally-derived immunity to BVDV and other respiratory viruses and their effect on humoral immune responses to vaccination in young calves. In the initial study, the duration and decay of specific antibodies to BVDV 1, BVDV 2, bovine herpesvirus 1 (BoHV-1), bovine respiratory syncytial virus (BRSV) and bovine parainfluenza 3 virus (PI3V) was evaluated in dairy calves that received maternal colostrum or a colostrum replacement product at birth. The duration of maternal immunity against BVDV and the other respiratory viruses in calves that received maternal colostrum was significantly variable. Additionally, a higher proportion of calves in the maternal colostrum group became seronegative to BVDV 1 and BVDV 2 earlier in life. In contrast, calves that received the colostrum replacement product had a more uniform and prolonged duration of maternally-derived immunity to BVDV 1 and BVDV 2. In a second study, early weaned beef calves that received maternal colostrum naturally from their dams and with different levels of maternally-derived immunity to BVDV were vaccinated at weaning at a median age of 72.2 days with three different multivalent, modified live virus (MLV) vaccines containing BVDV 1 and BVDV 2. Forty-five days after vaccination all calves were challenged with BVDV 2. The proportion of calves that seroconverted after vaccination was minimal; however, differences in the ability of vaccines to induce antibody responses were detected. Calves with higher antibody titers to BVDV1 and BVDV 2 before challenge had a lower proportion of calves that became viremic and shed BVDV in nasal secretions compared with controls. In a third study, early weaned beef calves that received maternal colostrum naturally from their dams and with different levels of maternally-derived immunity to BVDV and BoHV-1 were vaccinated at weaning at a median age of 93.5 days with four different multivalent, modified live virus (MLV) vaccines containing BVDV 1, BVDV 2, and BoHV-1. Forty-five days after vaccination calves were simultaneously exposed to 6 cattle persistently infected (PI) with BVDV and 8 calves acutely infected with BoHV-1. Differences in the ability of vaccines to induce antibody responses to BVDV but not to BoHV-1 were detected; however, clinical disease was not observed among calves after exposure to BVDV and BoHV-1. Groups with higher mean antibody responses to BVDV 1 and BVDV 2 after vaccination demonstrated a decreased proportion of calves with viremia and BVDV shedding compared with groups with lower mean antibody responses to BVDV 1 and BVDV 2. Viremia or BoHV-1 nasal shedding was not detected among calves at any time during the study.